Short-Term Investments - Schedule of Fair Values and Gross Unrealized Losses (Aggregated by Investment Category) of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	$ 14,027	$ 2,249
Gross Unrealized Losses	(16)	(2)
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	5,694
Gross Unrealized Losses	(1)
Corporate notes and bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	67,220	14,296
Gross Unrealized Losses	(101)	(40)
U.S. agency obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	40,549	82,806
Gross Unrealized Losses	(51)	(54)
U.S. treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	68,704	33,486
Gross Unrealized Losses	$ (111)	$ (37)